1. Field of the Invention
This invention relates generally to solderless electrical connectors of the open-ended deformable type and, more particularly, to such connectors which incorporate conductor insulation-piercing protuberances and inner perforable insulative liners, and to methods of fabrication therefor.
2. Description of the Prior Art
Electrical connectors of the solderless, open-ended type, incorporating a pair of coaxially positioned and deformable sleeves, confined within an outer insulative jacket, have been employed for many years to provide reliable electrical connections between insulated conductors inserted therewithin. Such connectors have found extensive use, particularly in the communications industry, in the splicing or joining of diverse conductors and/or cables such as employed in telephone switching equipment.
One early type of such a connector is disclosed in U.S. Pat. No. 3,064,072, of H. J. Graff et al. As disclosed therein, an inner metallic sleeve, preferably made of hard, spring-tempered metal, is formed with a plurality of preformed, spaced apart perforations defining inwardly extending protuberances, such as in the form of prongs or tangs. These protuberances are dimensioned and arranged so as to pierce the insulation of insulated conductors after the latter have been inserted within the inner sleeve, and in response to a crimping force exerted on the outer insulative jacket. The outer sleeve of the Graff et al connector is formed of a relatively soft, malleable material that will result in that sleeve remaining in a deformed configuration after the connector has been crimped. This insures that the protuberances of the inner sleeve, of spring-like material, will remain in reliable, permanent, biting contact with the metallic core portions of the insulative conductors.
Notwithstanding the many attributes of connectors of the above-described type, there has been a troublesome and well recognized problem encountered in their use heretofore when constructed as thus far described. More specifically, because of the presence of the inwardly extending protuberances formed in the inner sleeve, the free-ends of conductors have had a tendency to hang-up on the protuberances while being telescopically inserted within the open end of the connector to the desired depth. While back and forth motion of the conductors, generally accompanied with a slight tilting or skewing thereof, will normally free the ends from obstructing protuberances, this is time consuming, and often results in an assembler in the field not always knowing if the free end of each inserted conductor has actually bottomed.
One approach taken to resolve this problem heretofore has involved inserting a strip of thin, insulative film, folded into a U-shaped configuration, within the bore of the inner sleeve of open-ended connectors of the type in question. Such an inserted film functions as a perforable liner, by initially overlying the distal ends of at least the majority of the protuberances and, thereby, provides a relatively smooth wall surface for receiving the free ends of the conductors.
U.S. Pat. No. 3,784,731, of Thomas Newbold discloses one such U-shaped liner that is retained within the inner sleeve by reversibly bent external extensions which are sandwiched between the outer surface of the outer metallic sleeve and the inner surface of the insulative jacket of the composite connector. Such a liner and technique for supporting it disadvantageously requires considerable manipulating of the liner during assembly, and necessitates a separate, time consuming operation, as well as specialized and relatively expensive apparatus is performed in a high volume, automated manner.
A somewhat different approach to supporting a similar loosely positioned U-shaped liner is disclosed in U.S. Pat. No. 3,839,595, of John L. Yonkers. In one preferred embodiment of that reference, outer free ends of the liner that extend beyond the open end of the connector are folded back against an outer flange area of the jacket and secured thereagainst, preferably by a separate elastic band. The need for such an auxiliary band not only increases the total costs of the liner, but is also time consuming in that it requires both an additional assembly operation, and rather expensive and complex liner and band assembly apparatus. In addition, such elastic bands have a tendency to become detached from the outer flange of the jacket due to external conditions, such as vibration during parts feeding or shipment, or handling in the field.
Regardless how the outer folded-back leg portions are secured to the connector, the loose, inner leg portions of the liner have a tendency to become wrinkled and, thereby, produce their own form of obstruction either at the open end of the connector, or at some point inwardly therealong. When that happens, the liner may very readily compound the very problem which it was intended to obviate, namely, preventing the protuberances from obstructing the free ends of conductors when inserted within the connector.
The general configuration of the aforementioned U-shaped liners employed heretofore have also been found wanting in a number of other material respects. More specifically, because of the relatively small inside dimensions of the inner sleeve bore, typically being of the order of 0.050 inch by 0.110 inch when elliptical in shape, it is very difficult, even with sophisticated assembly apparatus, to reliably and consistently insert a strip of relatively thin plastic film within the sleeve so as to overlie all of the protuberances. To accomplish this, the two major U-shaped leg portions must not be fully inserted within the inner sleeve, but have their mutually disposed and longitudinally extending leg portion edges ideally in mating relationship so as to form a liner with an essentially continuous circumferentially and longitudinally extending wall area. This is important if the liner is to overlie the distal ends of all of the protuberances, as the latter typically are formed in a continuous circumferential array about the inner surface of the inner sleeve. If the linerdefining plastic strip should become slightly misaligned while being inserted within the sleeve, or if it is intentionally made wider than ideally necessary to insure that it is completely contiguous with the inner surface of the associated sleeve, then the longitudinal edges of the major leg portions would necessarily overlap so as to further restrict the effective bore dimensions of the sleeve.
Another disadvantage of U-shaped liners is that the amount of film material required therefor must be substantially larger than that actually required to overlie the array of protuberances because of the generally employed outer folded-back leg portions. Even when the latter are not employed, however, the U-shaped liners proposed and utilized heretofore have at least had extended leg portions that are secured to the inner surface of the jacket adjacent the open end thereof (as distinguished from being secured to the upper peripheral edge region of the inner sleeve). Such liner securement has the disadvantage of further restricting the effective bore of the connector, by exposing the peripheral edge of the liner as an additional obstruction to the free ends of conductors when inserted therewithin.
A different approach taken heretofore to obviate the problem of inserting conductors within a deformable openended connector having sharp, inwardly extending protuberances has resulted in the so-called channel type connector, characterized by having a completely open side as assembled. The advantage of such a connector, in the absence of any type of liner, is that conductors may be readily inserted laterally into the recessed channel area of the conductor with a minimal amount of obstruction by insulation-piercing protuberances formed therein.
One connector of the aforementioned open-sided type is disclosed in U.S. Pat. No. 3,410,950, of W. P. Freudenberg. In connection with the channel member of that connector, a thin plastic film is employed to cover both the inner and outer surfaces of and, thereby, hermetically seal the member therewithin. The purpose of the film, it should be noted, is not to facilitate the insertion of conductors within the recessed area thereof (as one side of the assembled conductor is completely open), but rather, to allow a sealing paste to be initially confined adjacent the protuberances, and to thereafter effect a permanent hermetic seal when the film is ruptured. More specifically, upon the crimping of the channel-forming connector about one or more insulated wires inserted laterally therewithin, the inner film is ruptured and the sealant flows around, and seals, the interface between the wire and the connector projections.
Freudenberg suggests that the inner film, which necessarily overlies the protuberances extending upwardly from the base of the channel member, may be applied and secured to select inner surface areas thereof by a wellknown vacuum forming or drawing technique. This technique involves laying the film over the open side of the channel member and then drawing the film downwardly against the inner side walls thereof by applying a partial vacuum (through openings in the channel member) to the underside of the film.
Unfortunately, such a vacuum drawing technique would be totally ineffective with respect to the inserting of a thin section of film into a fabricated open-ended sleeve, with the film thereafter being drawn into the desired circumferentially and longitudinally disposed liner configuration. This follows, in part, from the fact that the depth of the draw is substantially greater than the narrowest width dimension of the sleeve, hence the amount of vacuum required would be excessive. Moreover, the fabricated sleeve is not only open at both ends, but substantially porous over a substantial wall portion thereof. Thus, an effective vacuum would be almost impossible to establish for any type of film assembly operation to be performed therewithin.
In addition, a vacuum drawing technique also does not readily lend itself to the securing of either an adhesive backed or heat-sensitive ionomer film, for example, to sleeves even while still in a partially fabricated strip stock configuration (conducive to an automated fabricating process, such as carried out with progressive punch and die apparatus), for several reasons:
First, the only areas of a planar sleeve section that a film could be effectively vacuum drawn against would be the distal ends of the perforation-formed protuberances. This could lead to detrimental premature rupturing of the film.
Secondly, and equally important, is the fact that in order for any film-defining liner for sleeves of the open-ended type not to present an open end obstruction itself, the liner must either (1) include leg extensions, so as to provide a smooth, tapered wall transition extending inwardly of the normally necked-down jacket region, or (2) in some way be firmly and reliably secured to the unperforated, circumferentially disposed open end region of each sleeve as fabricated.
The first mentioned liner assembly condition, of course, is accomplished with U-shaped liners that are folded back outside the open end of the connector jacket. As to the second alternative liner assembly condition, a vacuum drawing technique could not be relied upon because of the solid wall construction of the sleeve between the border edges thereof and the adjacent perimeter of the array of protuberances. Such border areas are required, of course, not only to give the fabricated sleeve the necessary rigidity, but to prevent the formation of sharp, jagged edges that would otherwise result from partially formed perforations along the peripheral edges of the sleeve.
It thus becomes readily apparent that a vacuum drawing, film securing technique of the type disclosed in the Freudenberg patent, which, it should be noted, is only intended for use in hermetically sealing open-sided connectors, would be completely ineffective for use in the fabrication of open-ended sleeves, either during or after the fabrication of same. Notwithstanding that fact, such a connector, even with such a deposited film that inherently could function as a liner therein, has a number of disadvantages as compared to the open-ended, telescopically disposed sleeve type connector. For example, the open-sided connector is generally more difficult for an installer to handle and manipulate while inserting conductors therewithin to effect an electrical connection. Open-sided connectors also have a tendency to become entangled while in bulk form, and generally require more tooling to produce the necessary double-sided walls and protuberances during manufacture, as well as more complex tooling to effect the crimping thereof to effect a subsequent electrical connection with conductors mounted therewithin. Such connectors, of course, also do not readily lend themselves to being taped in pairs between upper and lower flexible transporting tapes, for example, so as to not only allow automated transport of the connectors to a cable or wire splicing station, but to allow the cables or wires in pairs to be telescopically inserted therein.
For the foregoing reasons, the open-ended, sleevetype connector with a perforable U-shaped film strip has gained much greater acceptance in the communications industry heretofore than the open-sided type, with or without an insulative film encapsulating the channel thereof.
What has nevertheless remained as a serious impediment to the otherwise very advantageous attributes and features of the open-ended B-wire type of connector, when incorporating an internal U-shaped liner, has been the difficulty, time and expense involved heretofore in assembling such a liner within the inner insulation-piercing sleeve after the latter has been completely fabricated.